The present invention relates generally to high data rate communication systems. More particularly, the present invention is related to a system and method of extracting information from pulse-position modulated (PPM) signals.
Existing high data rate optical networks, such as the Internet backbone networks embody OC-192 or OC-768 standards, which have data transfer rates of 10 Gbit/s and 40 Gbits/sec, respectively. The existing networks typically rely upon a clock and a data recovery scheme that utilizes amplitude modulation (AM).
The available signal-to-noise ratios and the lengthy transmission distances involved within these systems have limited the modulation formats and have necessitated a high degree of error-correction coding overhead. The modulation has been limited to one bit per symbol ON-OFF keying. The error-correction coding overhead allows for the bit-error rates that are required of the Internet networks.
The general approach to obtaining the higher data rates in Internet networks and the like has been to increase the clock rate and to focus engineering attention on solving the problems associated with the transmitting and receiving of ever-higher bandwidths, which are associated with higher data rates. In general, even without transmitting and receiving at high data rates, AM systems are sensitive to attenuation and amplitude type noise, which degrades the signal-to-noise ratio. The AM systems also tend to exhibit power and signal losses. In AM systems when data rates are increased noise sensitivity and signal losses tend to increase. Signal losses can include dielectric loss and skin-effect loss, as well as loss from connectors, line impedance mismatches, series capacitors, passive equalizers and pulse shaping, and differential and signal ended transmissions, or signal transmissions.
Some other available communication systems incorporate the use of pulse-position modulation (PPM) for the transmission and reception of data. PPM does not exhibit the same noise and signal losses as that of AM type systems. Since signals are modulated in time, the signals are less sensitive to amplitude noise and power losses. However, PPM systems are constrained by receiver accuracy to significantly lower data rates. Current PPM systems monitor positions of pulses within time slots. As data rates increase, width of the time slots decreases, resulting in the need for a more accurate receiver.
Several PPM type communication systems do exist that are capable of receiving the high data rates, but unfortunately these systems rely upon optical techniques that require hardware that is complex, costly, and of a large physical form factor.
Thus, there exists a need for an improved PPM receiver and method of extracting information from PPM signals that supports high data rates, has high signal-to-noise performance, is robust, simple, inexpensive, and has reduced form factor size.